1. Field of the Invention
The present invention relates to a filter inspection method which can be used to detect defects such as holes or cracks generated in a porous filter, and a filter inspection apparatus.
2. Description of the Related Art
A porous filter has numerous pores, and passes a fluid to be treated through the pores, to filter the fluid. For example, a honeycomb structure made by porous partition walls captures a particulate matter included in an exhaust gas discharged from a car engine or the like, by the partition walls, whereby the exhaust gas purified by passing through the partition walls is discharged to the outside from the honeycomb structure.
If holes, cracks and the like are present in the porous filter, a substance to be actually captured passes through the filter owing to these holes, cracks, and the like, which impairs a filtering function. Thus, in the porous filter, the holes or the cracks become defects which deteriorate the function of the filter. Consequently, there have been disclosed a method of inspecting the presence/absence of defects such as the cracks and holes in the porous filter, and an inspection apparatus (Patent Documents 1 to 3).
In the Patent Documents 1 to 3, there have been disclosed an inspection method of introducing fine particles into a filter, and detecting the fine particles passed through the filter, to check the presence/absence of defects such as the holes and the cracks in the filter, and an inspection apparatus.
As the fine particles for use in the above inspection, fine particles generated by burning incense and the like (e.g., Patent Document 1) or water particles having particle diameters of several hundreds of microns or smaller (e.g., Patent Documents 2 and 3) are used.    [Patent Document 1] JP-A-2002-357562    [Patent Document 2] JP-A-2004-286703    [Patent Document 3] JP-A-2009-115655